The effect of hydroxyurea on the phosphorylation of zidovudine and lamivudine in human umbilical vein endothelial cells.

The purpose of this study was to characterize the activation of zidovudine (ZDV) and lamivudine (3TC) in human umbilical vein endothelial cells (HUVEC) with and without hydroxyurea (HU) pretreatment. HUVEC were pretreated with HU or control media for 24 h and then incubated for an additional 3 h with ZDV or 3TC. Intracellular concentrations of parent drugs and the phosphorylated forms were determined by high-performance liquid chromatography. Pretreatment with HU resulted in more than a threefold increase in intracellular concentrations of total ZDV, with the major intracellular form being the monophosphate (>80%). The relative percentage of each ZDV form was similar between control and HU-treated cells. On the other hand, intracellular concentrations of total 3TC increased only slightly (14%) with HU pretreatment. Although the parent drug remained the major intracellular form of 3TC, there was nearly a 400% increase in the 3TC triphosphate after HU pretreatment. These data demonstrate that HU causes a large increase in the intracellular accumulation of total ZDV, whereas it increases total 3TC only slightly but improves its triphosphorylation. Given the increase in intracellular concentrations of ZDV monophosphate after HU pretreatment and that the monophosphate has no antiviral activity but is associated with toxicity, the use of HU is not a good strategy to improve ZDV activation in human endothelium. There is improved production of the active antiviral 3TC triphosphate with HU pretreatment. The combination may be beneficial in treating potential sanctuary sites such as endothelium.